Compressive Surfaces For Ultrasonic Tissue Scanning

ABSTRACT

Automated ultrasonic scanning of a chestwardly compressed breast of a supine patient uses a scanning assembly that moves down to compress the breast through a membrane that is secured to the assembly across a bottom opening. A motorized ultrasound transducer moves across the breast while the breast remains downwardly compressed against the patient&#39;s chest, sending and receiving ultrasound energy through the membrane. The membrane is porous with respect to an acoustic coupling liquid that impregnates it. The transducer outputs ultrasound information that is processed to form initial planar images and then reconstructed slice images of breast tissue.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/702,202, filed Jul. 25, 2005, and U.S. Provisional Application No.60/1713,322, filed Aug. 31, 2005, each of which is incorporated byreference herein.

FIELD

This provisional patent specification relates to medical imaging. Moreparticularly, this provisional patent specification relates to thefacilitation of ultrasonic tissue scanning.

BACKGROUND

Volumetric ultrasound scanning usually involves the movement of anultrasound transducer relative to a tissue sample and the processing ofresultant ultrasound echoes to form a data volume representing at leastone acoustic property of the tissue sample. Although several examplesherein are presented in the particular context of human breastultrasound, it is to be appreciated that the present teachings arebroadly applicable for facilitating ultrasonic scanning of anyexternally accessible human or animal body part (e.g., abdomen, legs,feet, arms, neck, etc.). Moreover, although several examples herein arepresented in the particular context of mechanized scanning (i.e., inwhich the ultrasound transducer is moved by a robot arm or otherautomated or semi-automated mechanism), it is to be appreciated that oneor more aspects of the present teachings can be advantageously appliedin a handheld scanning context.

Volumetric ultrasound scanning of the breast has been proposed as acomplementary modality for breast cancer screening as described, forexample, in the commonly assigned US 2003/1007598A1 published Jan. 9,2003, which is incorporated by reference herein. The commonly assignedWO 2004/030523A2 published Apr. 15, 2004, which is incorporated byreference herein, describes a full-field breast ultrasound (FFBU)scanning apparatus that compresses a breast along planes such as thecraniocaudal (CC) plane, the mediolateral oblique (MLO) plane, etc., andultrasonically scans the breast. One side of an at least partiallyconformable, substantially taut membrane or film sheet compresses thebreast. A transducer translation mechanism maintains an ultrasoundtransducer in contact with the other side of the film sheet whiletranslating the ultrasound transducer thereacross to scan the breast.

Other FFBU scanning devices that compress the breast in otherdirections, such as in generally chestward or “head-on” directions, aredescribed in one or more of the following commonly assignedapplications, each of which is incorporated by reference herein: U.S.Ser. No. 60/565,698 filed Apr. 26, 2004; U.S. Ser. No. 60/577,078 filedJun. 4, 2004; U.S. Ser. No. 60/629,007 filed Nov. 17, 2004; WO2005/104729A2 published Nov. 10, 2005; and WO 2005/120357A1 PublishedDec. 22, 2005. It would be desirable to facilitate ultrasound scanningof a tissue volume (such as, but not limited to, a breast) in a mannerthat further improves image quality. Other issues arise as would bereadily apparent to one skilled in the art in view of the presentdisclosure.

SUMMARY

In one embodiment, an apparatus and related methods for ultrasonicallyscanning a tissue sample are provided, the apparatus comprising anultrasound transducer and a taut fabric sheet compressing the tissuesample, the ultrasound transducer contacting the taut fabric sheet andultrasonically scanning the tissue sample therethrough. Preferably, thetaut fabric sheet is substantially porous with respect to an acousticcouplant.

In another embodiment, an apparatus and related methods forultrasonically scanning a tissue volume having a tissue surface isprovided, comprising an ultrasound transducer and a vented membrane. Thevented membrane has a first surface contacting the tissue surface and asecond surface opposite the first surface. The ultrasound transducercontacts the second surface and is translated across the second surfacefor ultrasonically scanning the tissue volume. An acoustic couplant isapplied to one of the tissue surface, the first surface, and the secondsurface, the vented membrane being substantially porous with respect tothe acoustic coupling agent. The vented membrane has a void patternproviding this porosity.

As used in accordance with one or more of the embodiments, acouplant-porous material sheet, i.e., a couplant-porous fabric sheet ora vented membrane, promotes dissipation of air bubbles that mightotherwise form in the acoustic couplant at the compressive surfacewhich, in turn, promotes enhanced image quality, and furthermorepromotes locational stability of the tissue surface by virtue of thematerial textures provided. Other advantages are brought about as wouldbe apparent to one skilled in the art in view of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a perspective view of a full-field breast ultrasound(FFBU) scanning apparatus according to an embodiment;

FIG. 2 illustrates a perspective view of ultrasonic breast scanningusing the FFBU of FIG. 1 according to an embodiment;

FIG. 3 illustrates a taut fabric sheet according to an embodiment;

FIG. 4 and FIGS. 5A-5B illustrate a side view of ultrasonic breastscanning using the taut fabric sheet of FIG. 3;

FIG. 6A illustrates a fabric sheet in a generally relaxed (non-taut)state;

FIG. 6B illustrates the fabric sheet of FIG. 6A in a taut state whileunderlying tissue is being scanned therethrough in accordance with anembodiment;

FIG. 7 illustrates a taut fabric sheet having one or more visiblemarkings according to an embodiment;

FIG. 8 and FIGS. 9A-9D illustrate some of the many different overalldevice configurations in which taut fabric sheets according to thepresent teachings can be used for facilitating ultrasonic breastscanning;

FIGS. 10-13 illustrate one or more vented membranes according to one ormore of the embodiments;

FIGS. 14A-14B illustrate one or more vented membranes according to oneor more of the embodiments; and

FIGS. 15A-15B illustrate a top view and a side cut-away view,respectively, of a volumetric scanning probe according to an embodiment.

DETAILED DESCRIPTION

In one embodiment, the taut fabric sheet compresses the tissue sample tohave a generally planar shape, the ultrasound transducer beingtranslated along a generally planar path while scanning the tissuesample through the taut fabric sheet for volumetric scanning of thecompressed tissue sample. For this embodiment, the taut fabric sheet mayhave a minor degree of outward bulge due to the outward force of thetissue sample. For such embodiment, the ultrasound transducer may bedriven along a precisely planar path, thereby locally deforming the tautfabric sheet and the tissue sample by a small amount while passingthereover. Alternatively, the ultrasound transducer can be controlled soas to follow along the outward bulge in a conformal manner whilescanning the tissue sample through the taut fabric sheet.

In another embodiment, the taut fabric sheet compresses the tissuesample to have a desired three-dimensionally shaped surface, theultrasound transducer being translated to follow along thethree-dimensionally shaped surface while scanning the tissue samplethrough the taut fabric sheet. Preferably, the taut fabric sheet iswetted with an acoustic couplant facilitating acoustic coupling betweenthe ultrasound transducer and the tissue sample. Preferably, the tautfabric sheet is substantially porous with respect to the acousticcouplant to discourage the presence of air bubbles in an acoustic pathbetween the ultrasound transducer and the tissue sample. The taut fabricsheet may be wetted with the acoustic couplant by one or more of: (i)pre-impregnating the taut fabric sheet with the acoustic couplant; (ii)applying the coupling agent to a tissue-facing surface of the tautfabric sheet, or to the tissue surface, prior to compressing the tissuesample; (iii) applying the coupling agent to a transducer-facing surfaceof the taut fabric sheet prior to compressing the tissue sample; and(iv) applying the coupling agent to a transducer-facing surface of thetaut fabric sheet subsequent to compressing the tissue sample and priorto the scanning.

In one embodiment, the taut fabric sheet compresses the breast in agenerally head-on direction. In another embodiment, the taut fabricsheet compresses the breast along a standard x-ray mammogram plane(e.g., CC, MLO, LAT, etc.) The taut fabric sheet preferably compressesthe breast with a compressive force between about 2-20 lbs. Morepreferably, the taut fabric sheet compresses the breast with acompressive force of about 4-12 lbs. Even more preferably, the tautfabric sheet compresses the breast with a compressive force of about6-10 lbs.

As used herein, fabric refers generally to a material structure ofinterconnected parts, such as can be formed by knitting, weaving, orfelting natural or synthetic fibers, assembling natural or syntheticfibers together into an interlocking arrangement, fusing thermoplasticfibers, or bonding natural or synthetic fibers together with a cementingmedium, and further refers to materials having similar textures orqualities as those formed thereby, such as animal membranes or othernaturally occurring substances having fabric-like properties (eitherinherently or by processing), and such as materials generated bychemical processes yielding fabric-like webbings.

In one embodiment, the taut fabric sheet is substantially inelastic.Preferably, the taut fabric sheet is sheer to allow viewing of thecompressed tissue sample therethrough. One particularly suitablematerial for the taut fabric sheet comprises a polyester organzamaterial having a filament diameter of about 40 microns and a filamentspacing of about 500 microns. However, the taut fabric sheet maycomprise any of a variety of other fabrics that are substantiallyinelastic and generally porous to ultrasound couplants without departingfrom the scope of the present teachings. Examples include, but are notlimited to, polyester chiffon fabrics and cloth fabrics comprisingstraight weaves of substantially inelastic fibers. Where the weave isparticularly tight (for example, the cloth used in men's dress shirts orthe cloth used in many bed sheets), porosity can be achieved byperforating the cloth or otherwise introducing irregularities that allowthe ultrasound couplant to soak or seep through.

FIG. 1 illustrates a perspective view of a full-field breast ultrasound(FFBU) scanning apparatus 102 according to an embodiment, comprising aframe 104 that may contain an ultrasound processor, a movable supportarm 106, a compression/scanning assembly 108 connected to the supportarm 106 via a ball-and-socket connector 112, and a monitor 110 connectedto the support arm 106 at a joint 114. Preferably, the support arm 106is configured and adapted such that the compression/scanning assembly108 is either (i) neutrally buoyant in space, or (ii) has a light netdownward weight (e.g., 2-3 pounds) for breast compression, whileallowing for easy user manipulation.

Compression/scanning assembly 108 comprises a taut fabric sheet 118 forcompressing a breast, the taut fabric sheet 118 having a bottom surfacecontacting the breast while a transducer is swept across a top surfacethereof to scan the breast. Optionally, the support arm 106 may comprisepotentiometers (not shown) to allow position and orientation sensing forthe compression/scanning assembly 108, or other types of position andorientation sensing (e.g., gyroscopic, magnetic, optical, radiofrequency (RF)) can be used. Within frame 104 may be provided a fullyfunctional ultrasound engine for driving an ultrasound transducer andgenerating volumetric breast ultrasound data from the scans inconjunction with the associated position and orientation information.The volumetric scan data can be transferred to another computer systemfor further processing using any of a variety of data transfer methodsknown in the art. A general purpose computer, which can be implementedon the same computer as the ultrasound engine, is also provided forgeneral user interfacing and system control. The general purposecomputer can be a self-contained stand-alone unit, or can be remotelycontrolled, configured, and/or monitored by a remote station connectedacross a network.

FIG. 2 illustrates one example of how the compression/scanning assembly108 including the taut fabric sheet 118 may be used for ultrasonicbreast scanning. An ultrasound transducer 202 housed within thecompression/scanning assembly 108 is swept across the breast asillustrated. Preferably, the taut fabric sheet 118 is wetted with anacoustic couplant facilitating acoustic coupling between the ultrasoundtransducer and the tissue sample. Preferably, the taut fabric sheet 118is substantially porous with respect to the acoustic couplant todiscourage the presence of air bubbles in an acoustic path between theultrasound transducer and the tissue sample.

In one embodiment, the fabric sheet is pre-impregnated with the acousticcouplant. In another embodiment, the fabric sheet is not pre-impregnatedwith the acoustic couplant Using a non-pre-impregnated (i.e., dry)fabric sheet is advantageous in that it is easier for the technician tosee the breast therethrough during breast positioning as compared tousing a pre-impregnated fabric sheet. For embodiments in which a chiffonor organza fabric is used, it has been found that applying the acousticcouplant directly to the breast, and then bringing the fabric sheet intotaut, compressible contact with the couplant-coated breast, yieldsparticularly good image quality.

In one embodiment, the fabric sheet is a permanent or semi-permanentcomponent of the FFBU scanner, and is sterilized after each patient. Inanother embodiment, the fabric sheet is disposable or recyclable, and isreplaced after each patient. By way of example, the fabric sheet can berolled up onto a long roll that is attached to the frame of thecompressive member, and that roll can be progressively advanced betweenpatients such that each patient uses a fresh piece of the fabric sheet.Assemblies can be provided as needed to tension, release, and re-tensionthe fabric sheet.

Several advantages are realized by using a taut fabric sheet that issubstantially porous to acoustic couplant liquid according to thepresent teachings. First, the taut fabric sheet promotes dissipation ofair bubbles that might otherwise form in the acoustic couplant at themembrane surface. As compared to using a material nonporous to theacoustic couplant, image quality is increased by virtue of fewer airbubbles being present between the ultrasound transducer and the tissuesurface. Second, the surface textures of the taut fabric sheet promotelocational stability of the tissue surface, the skin being at leastpartially “grabbed” by the textures. The breast is thereby inhibitedfrom slipping or sliding along the compressive surface. This makespatient and breast positioning easier, and also reduces the possibilitythat the breast may slip while the transducer is being translated.Third, the flattening or compression of the breast, which is achievedusing the taut fabric sheet, in turn provides for thorough volumetricimaging and/or standardized volumetric imaging as described in US2003/007598A1 and WO 20041030523A2, supra. The scanned breast volumemay, if desired, be easily visualized by viewing an array of thick-sliceimages of slab-like subvolumes generally parallel to the plane ofcompression. Other advantages are brought about as would be apparent toone skilled in the art in view of the present disclosure. For example,in embodiments for which the taut fabric sheet is sheer (i.e., thin,fine, and relatively transparent), easier viewing of the breast isprovided therethrough (as compared to using a relatively opaque fabric),which further facilitates patient positioning and monitoring of theprogress and/or quality of the scanning process.

FIG. 3 illustrates a taut fabric sheet 302 according to an embodiment,the taut fabric sheet 302 being attached to a frame 304. In thisembodiment, the fabric material is already provided in a taut state astensionably mounted to the frame 304. This can be contrasted with atleast one other embodiment Infra in which the fabric material isprovided in a relaxed state, and becomes taut as the breast iscompressed.

FIG. 4 illustrates the taut fabric sheet 302 compressing a breast 402according to an embodiment. Although generally planar, the taut fabricsheet 302 exhibits some degree of outward bulging or bowing due to theupward force of the breast 402 thereagainst. An ultrasound transducer404 is poised to scan the breast 402 by being swept over the taut fabricsheet 302 in contact therewith.

FIG. 5A illustrates the taut fabric sheet 302 and ultrasound transducer404 according to one embodiment, wherein the ultrasound transducer 404is maintained strictly on a planar path 502 during the scanning processdespite the outward bulging of the taut fabric sheet 302. In thisembodiment, there is a local deformity 503, usually small, around thecurrent position of the ultrasound transducer 404. FIG. 5B illustratesthe taut fabric sheet 302 and ultrasound transducer 404 according toanother embodiment, wherein the ultrasound transducer 404 ismechanically controlled so as to follow 504 along the outward bulge in aconformal manner while scanning the breast 402 through the taut fabricsheet 302.

FIG. 6A illustrates a fabric sheet 602 as provided for use in anultrasound scanning apparatus according to an embodiment, wherein thefabric sheet is provided in a generally relaxed (non-taut) state. Frameelements 604 are provided on each side of the fabric sheet 602. In otherembodiments, the frame elements 604 can be replaced by roller elementsthat feed and receive new fabric, or by a variety of other framingconfigurations. In still other embodiments, the frame elements 604 canform a single frame similar to the frame 304 of FIG. 3. In each caseaccording to the embodiment of FIGS. 6A-6B, the fabric sheet isinitially in a relaxed/limp/non-taut state, and then the frame elementsare manipulated relative to the breast 402 such that the fabric sheet602 is placed into a taut state that compresses the breast 402, asillustrated in FIG. 6B.

In the example of FIG. 6B, the taut fabric sheet 602 compresses thetissue sample into a shape resembling a longitudinally-extending sectorof a cylinder. More generally, the breast may be compressed to have adesired three-dimensionally shaped surface (e.g., spheroidal,ellipsoidal, etc.). As illustrated in FIG. 6B, an ultrasound transducer604 may be translated to conformally follow along thethree-dimensionally shaped surface while scanning the tissue samplethrough the taut fabric sheet. As with other embodiments, theembodiments of FIGS. 6A-6B are not limited to scenarios in which thetissue sample is a breast. For example, embodiments similar to FIGS.6A-6B may be suitable and/or adaptable for compressive ultrasonicimaging of the arm, the leg, the neck, the abdomen, or other body part.

FIG. 7 illustrates a taut fabric sheet 702 according to an embodiment,wherein one or more visible markings 704 are provided for facilitatingpositioning of the taut fabric sheet 702 relative to the tissue surface.In the embodiment of FIG. 7, the visible demarcations are used to showwhere the nipple of a breast should be placed. In other embodiments, thevisible demarcations can be used to show other useful information suchas the scan center, scan borders, preferred orientations, preferredlocations for palpable lesions, etc., and/or for providing instructionalnotations, arrows, text, and the like.

FIG. 8 and FIGS. 9A-9D illustrate some of the many differentconfigurations in which taut fabric sheets according to the presentteachings can be used for facilitating ultrasonic breast scanning. FIG.8 illustrates an FFBU scanner 802 that is particularly adapted forobtaining ultrasound scans while the breast is compressed alongmammogram-like view planes such as the CC and MLO views, comprising acompression/scanning assembly 804 and a compressor 806 that can becollectively rotated among CC, MLO, and LAT orientations. Thecompression/scanning assembly 804 comprises a taut fabric sheet 808similar to those described supra and yielding similar advantages. In theparticular orientation of FIG. 8, the CC compression view is obtained byscanning in an upward direction through the taut fabric sheet 808. FIGS.9A-9D illustrate how a taut fabric sheet 904 may be advantageously usedas part of a leaning-forward prone scanning device 902 (FIGS. 9A-9B), alying-down prone scanning device 902′ (FIG. 9C), and an upright scanningdevice 902″ (FIG. 9D).

Whereas many alterations and modifications of the present invention willno doubt become apparent to a person of ordinary skill in the art afterhaving read the foregoing description, it is to be understood that theparticular embodiments shown and described by way of illustration are inno way intended to be considered limiting. By way of example, it is tobe appreciated that any of a variety of different frame assemblies canbe used that position, tension, and otherwise manipulate the fabricsheet, whether the fabric sheet is permanently used and re-used fordifferent patients or is disposable for each patient, without departingfrom the scope of the present teachings.

By way of further example, for certain alternative embodiments in whichthe fabric sheet is a woven material, the weave may optionally comprisedifferent materials woven in different directions (for example, ainelastic polyester fiber in one direction and a partially elastic fiberin another direction) such that the amount of tautness is directionallydependent. Therefore, reference to the details of the embodiments arenot intended to limit their scope.

Also provided as an alternative to, or for use in conjunction with, thetaut fabric sheet based system described above is an apparatus andrelated methods for ultrasonically scanning a tissue volume having atissue surface, comprising an ultrasound transducer and a ventedmembrane. The vented membrane has a first surface contacting the tissuesurface and a second surface opposite the first surface. The ultrasoundtransducer contacts the second surface and is translated across thesecond surface for ultrasonically scanning the tissue volume. Anacoustic couplant is applied to one of the tissue surface, the firstsurface, and the second surface, the vented membrane being substantiallyporous with respect to the acoustic coupling agent for discouraging thepresence of air bubbles in an acoustic path between the ultrasoundtransducer and the tissue surface during the ultrasound scan. The ventedmembrane has a void pattern providing this porosity. Preferably, thevoid pattern is configured such that the vented membrane locationallystabilizes the tissue surface against movement during tissue positioningand transducer translation.

In one embodiment the void pattern is spatially uniform. In anotherembodiment, the void pattern is spatially varying and defines one ormore visible markings for facilitating positioning of the ventedmembrane relative to the tissue surface. Preferably, the size of thevoids (and the void pitch) is equal to or greater than the wavelength ofthe acoustic signals being applied. By way of example, for a 7 MHzultrasound frequency, the size of the voids should be about 0.5 mm orgreater.

In one embodiment, the vented membrane is formed by (a) forming auniform film sheet, and (b) establishing a void pattern into the uniformfilm sheet by one of stamping, perforating, or other process designed toestablish a void pattern. Examples include laser perforation,perforation using hot needles, die cutting, cold stamping, andhot-stamping.

In one embodiment, the vented membrane is substantially taut andcompresses the tissue surface toward a flattened state, the ultrasoundtransducer being mechanically translated within a single plane. Inanother embodiment, the vented membrane is flexible and configured tosubstantially conform upon or around the tissue surface, the ultrasoundtransducer being translated across the second surface in a manner thatfollows a contour thereof when so conforming upon or around the tissuesurface. By way of non-limiting example, if the tissue volume is a humanbreast, the vented membrane may conform in a bra-like fashion around thebreast contours.

With reference again to FIG. 1 and FIG. 2, supra, the element 118 canalternatively comprise an at least partially conformable vented membranein a substantially taut state, the vented membrane having a bottomsurface contacting the breast while a transducer is swept across a topsurface thereof to scan the breast. With reference again to FIG. 8 andFIGS. 9A-9D, supra, the elements 808 and 904 can alternatively comprisean at least partially conformable vented membrane in a substantiallytaut state, the vented membrane having a bottom surface contacting thebreast while a transducer is swept across a top surface thereof to scanthe breast.

Several advantages are realized by using a vented membrane according tothe present teachings. First, the vented membrane promotes dissipationof air bubbles that might otherwise form in the acoustic couplant at themembrane surface. As compared to using a non-vented membrane, imagequality is increased by virtue of fewer air bubbles being presentbetween the ultrasound transducer and the tissue surface. Second, ascompared to using a non-vented membrane, there is reduced attenuation(and reduced reflections) by virtue of the fact that there is lessmembrane material between the ultrasound transducer and the tissuesurface. Third, the presence of the void patterns in the vented membranepromotes locational stability of the tissue surface, the skin being“grabbed” by textures formed by the voids. The breast is therebyinhibited from slipping or sliding along the compressive surface. Thismakes patient and breast positioning easier, and also reduces thepossibility that the breast may slip while the transducer is beingtranslated. Other advantages are brought about as would be apparent toone skilled in the art in view of the present disclosure.

Examples of materials that can be used for the vented membrane include,but are not limited to, polypropylene, polyester (including but notlimited to Mylar), polyethylene, PTFE, PET, paper, Kevlar, metal, andepoxy-fiber composite materials. In one embodiment, the vented membraneis a permanent or semi-permanent component of the FFBU scanner, and iscleaned after each patient. In another embodiment, the vented membraneis disposable or recyclable, and is replaced after each patient. By wayof example, where the vented membrane comprises a Mylar film sheet orsimilarly flexible and thin material, the vented membrane material canbe rolled up onto a long roll that is attached to the frame of thecompressive member, and that roll can be progressively advanced betweenpatients such that each patient uses a fresh piece of the ventedmembrane material. Assemblies can be provided as needed to tension,release, and re-tension the vented membrane material.

FIG. 10 illustrates a vented membrane 1002 according to an embodiment,the vented membrane 1002 being attached to a frame 1004. The ventedmembrane 1002 may comprise a film sheet less than 1 mm thick, with atleast 25% of a surface area of the film sheet being occupied by voids.In another embodiment, at least 80% of the surface area is occupied byvoids. In one embodiment, the voids are circular with a uniform diameterbetween about 0.1 mm-25 mm and have a uniform pitch between about1.1-10.0 times the diameter. The voids may be arranged in regularlattice patterns (e.g., with unit cells being triangular, square,rectangular, pentagonal, hexagonal, etc) or, alternatively, in any of avariety of randomized arrangements. The randomness may be in terms ofvoid size, void shape, and/or void patterns and may serve to reduceartifacts that might arise at some acoustic frequencies due toshort-term or long-term lateral orderings in the vented membrane. Moregenerally, a wide variety of different void shapes, patterns, anddimensions are within the scope of the present teachings.

FIG. 11 illustrates a vented membrane 1102 according to an embodiment,the vented membrane 1102 being attached to a frame 1104. Referringfurther to FIG. 12, the vented membrane 1102 comprises a netting formedby a vertical fusing of a first monofilamental pattern 1252 and a secondmonofilamental pattern 1254. Preferably, at least 25% of a surface areaof the netting is occupied by voids. In another embodiment, at least 80%of the surface area is occupied by voids. In still another embodiment,the thickness of the monolilaments is about 0.04 mm at while the pitchis about 0.5 mm, providing for more than 90% of the area beingtransmissive (i.e., occupied by voids rather than material).

FIG. 13 illustrates a vented membrane 1302 according to an embodiment,wherein the void pattern is spatially varying and defines one or morevisible markings for facilitating positioning of the vented membranerelative to the tissue surface. Visible in the embodiment of FIG. 13 isa central area 1304 defined by differently-sized and/or differentlypositioned voids that can be used to show where the nipple of the breastshould be placed.

FIGS. 14A and 14B illustrate vented membranes according to anembodiment, wherein the void pattern is spatially varying and definesone or more visible markings for facilitating positioning of the ventedmembrane relative to the tissue surface. Visible in the embodiment ofFIGS. 14A and 14B are variations in the spacings of the monofilamentalelements to visibly delineate the center of a scan area. The visibledemarcation can be used to show where the nipple of the breast should beplaced, and/or where a palpable lesion can be placed. More generally,visible demarcations by variations In the void patterns according toFIGS. 13, 14A, and 14B can take on any of a variety of shapes, forms,and locations for any of a variety of purposes. Thus, for example, FIG.14B illustrates additional variations in the monofilamental elementspacings to demark the edge of the scan area.

In other embodiments, the vented membrane can have varying colors (e.g.,printing on the film sheet in FIG. 10, or using differently coloredmonofilamental elements in FIG. 11) to denote special locations such asthe scan center, scan borders, preferred orientations, preferredlocations for palpable lesions, etc., and/or for providing instructionalnotations, arrows, text, and the like. In still other embodiments,combinations of void pattern alterations and printing/coloring can beused to provide such positioning references, notations, etc.

In one embodiment, the vented membrane can be pre-impregnated with theacoustic couplant. In another embodiment, the vented membrane is notpre-impregnated with the acoustic couplant. Using a non-pre-impregnated(i.e., dry) vented membrane is advantageous in that it is easier for thetechnician to see the breast therethrough during breast positioning ascompared to using a pre-impregnated vented membrane. It has been foundthat applying the acoustic couplant directly to the breast, and thenbringing the vented membrane into contact with the couplant-coatedbreast, yields particularly good image quality. Generally speaking, moreacoustic couplant is needed as compared to the amount required with theuse of a non-vented membrane.

Whereas many alterations and modifications of the present invention willno doubt become apparent to a person of ordinary skill in the art afterhaving read the foregoing description, it is to be understood that theparticular embodiments shown and described by way of illustration are inno way intended to be considered limiting. By way of example, it is tobe appreciated that any of a variety of different frame assemblies canbe used that position, tension, and otherwise manipulate the ventedmembrane, whether the vented membrane is permanently used and re-usedfor different patients or is disposable for each patient, withoutdeparting from the scope of the present teachings.

By way of further example, while one or more of the embodiments supra isdescribed in terms of a relatively large amount of compressive forcebeing applied by the vented membrane (e.g., to flatten the breast in anx-ray mammogram-like fashion), in other embodiments the compressiveforce can be very light. For example, in an alternative embodiment, thevented membrane is configured and formed to be worn by the patient in abra-like fashion, and the ultrasound transducer is moved by a sensitiverobotic arm that follows the contours of the breast as maintained insidethe bra-like device. In such cases, the compressive forces exerted bythe vented membrane can be very light, even approaching zero in somelocations, being sufficient only to maintain contact with the skin atthose locations. In one alternative embodiment, the vented membrane cancomprise material similar to the porous gel bladder material(s)discussed in U.S. Pat. No. 5,626,554. Therefore, reference to thedetails of the embodiments are not intended to limit their scope.

FIGS. 15A-15B illustrate a top view and a side cut-away view,respectively, of a volumetric scanning probe 1500 according to anembodiment in which a flexible couplant-porous material sheet 1502,i.e., a flexible couplant-porous fabric sheet or a flexible ventedmembrane, is used as a compressive surface between an angularly rotatingtransducer head 1508 and a tissue surface 1530. The transducer head 1508is mounted at the periphery of a cylindrical roller 1504 driven by amotor/actuator 1510 in a manner that angularly sweeps the cylindricalroller 1504 back and forth between about −45 degrees and +45 relative toa normal to the tissue surface, the back and forth motion being at afrequency in a range of 0.25 Hz-4 Hz. Turnable members 1506 a and 1506 bkeep the sheet 1502 in a substantially taut state. Optionally, theturnable members 1506 a and 1506 b can be rollers that store asubstantial amount of sheet material 1502, and can progressively renewthe sheet material during a scan, and/or renew the sheet material on aper-patient basis for sanitation purposes.

Advantageously, the volumetric scanning probe 1500 can provide forinstantaneous or near-instantaneous volumetric images in the tissue neartransducer head 1508. Precision is facilitated by the material sheet1502, which provides for good acoustic coupling using an acousticwetting agent while also keeping the tissue locationally stableunderneath the roller 1504/transducer head 1508. For one embodiment,when the volumetric scanning probe 1500 is laterally translated acrossthe tissue surface, the turnable members 1506 a and 1506 b are turned byadditional actuators (not shown) to feed just the right amount of sheetmaterial 1502 such that there is no sliding of the sheet material 1502relative to the tissue surface. This is achieved by causing the materialsheet to be fed out (in mm/second) at the same speed that the volumetricscanning probe 1500 is being laterally translated across the tissuesurface.

Whereas many alterations and modifications of the present invention willno doubt become apparent to a person of ordinary skill in the art afterhaving read the foregoing description, it is to be understood that theparticular embodiments shown and described by way of illustration are inno way intended to be considered limiting. Therefore, reference to thedetails of the embodiments are not intended to limit their scope.

1-26. (canceled)
 27. An apparatus for ultrasonically scanning a chestwardly compressed breast of a patient, comprising: a support arm; and a compression/scanning assembly supported by the support arm and configured to move under operator control between a non-scanning position in which the assembly is out of contact with the patient's breast to a scanning position in which the assembly is in contact with the breast and compresses the breast chestwardly, wherein said compression/scanning assembly comprises: (i) a housing member supported by the support arm, said housing member having an opening; (ii) a compressive membrane secured to said assembly across at least a part of said opening of said housing member and positioned to contact the breast and compress the breast in a chestward direction as the compression/scanning assembly is moving into said scanning position, and to maintain the breast compressed when in said scanning position, wherein said compressive membrane is porous with respect to an acoustic coupling liquid; (iii) an ultrasound transducer disposed within the housing member; and (iv) a transducer translation mechanism disposed within the housing member and coupled to the ultrasound transducer, the transducer translation mechanism being configured to mechanically control the ultrasound transducer when said compression/scanning assembly is in said scanning position to maintain contact with said compressive membrane while scanning the breast through said compressive membrane.
 28. The apparatus of claim 27, the patient being supine and the breast being upwardly facing, the compression/scanning assembly being above the supine patient and out of contact with the upwardly facing breast when in said non-scanning position, the compression/scanning assembly moving downwardly into contact with the upwardly facing breast and into said scanning position, said opening in the housing member being a lower opening.
 29. The apparatus of claim 27, wherein said compressive membrane is a chiffon or organza fabric sheet.
 30. The apparatus of claim 27, wherein said support arm is an articulated, movable arm.
 31. The apparatus of claim 27, wherein said compressive membrane is disposable.
 32. The apparatus of claim 27, wherein said assembly is configured to move under hand control by the operator between said scanning and non-scanning positions.
 33. A method for ultrasonically scanning a breast of a patient, comprising: providing a compression/scanning assembly that includes a housing member having an opening and a compressive membrane secured to said assembly across at least a part of the opening, the compressive membrane being porous with respect to an acoustic coupling liquid, the compression/scanning assembly being supported by a support arm in a non-scanning position out of contact with the patient's breast; selectively manipulating the compression/scanning assembly from the non-scanning position out of contact with the patient's breast toward and into a scanning position in which the compressive membrane is in contact with the breast and compresses the breast in a chestward direction; impregnating the compressive membrane with acoustic coupling liquid before and/or after the assembly is in contact with the breast; after the compression/scanning assembly is in said scanning position and the compressive membrane is impregnated with acoustic couplant, scanning the breast through the acoustic couplant impregnated compressive membrane with a mechanically controlled ultrasound transducer contained within said housing member of the compression/scanning assembly, the ultrasound transducer being maintained in contact with said acoustic couplant impregnated compressive membrane while scanning the breast therethrough.
 34. The method of claim 33, the patient being supine and the breast being upwardly facing, said opening in the housing member being a lower opening, the non-scanning position of the compression/scanning assembly being above the supine patient and out of contact with the upwardly facing breast, and said selectively manipulating causing the compression/scanning assembly to move downwardly toward and into said scanning position in contact with the upwardly facing breast.
 35. The method of claim 33, wherein said providing comprises providing a compressive membrane comprising a chiffon or organza fabric sheet.
 36. The method of claim 33, wherein said proving comprises providing a support arm comprising an articulated, movable arm.
 37. The method of claim 33, wherein said providing comprises providing said compressive membrane in the form of a disposable member, the method further comprising: prior to said selectively manipulating, installing the disposable compressive membrane across said opening of said housing member; and subsequent to said scanning, removing the disposable compressive membrane from said housing and disposing of said disposable compressive membrane.
 38. A method of imaging a chestwardly compressed breast of a patient with ultrasound, comprising: providing a scanning assembly; removably securing at one side thereof a single-use membrane that is porous with respect to an acoustic coupling liquid or gel; moving the scanning assembly in a chestward direction toward a patient until the membrane contacts and chestwardly compresses a breast of the patient in a scanning position of said assembly; supplying said coupling liquid or gel to the membrane at one or more selected times relative to said moving of the scanning assembly; when the scanning assembly is in said scanning position, causing an ultrasound transducer in said assembly to scan the compressed breast through said membrane and liquid or gel supplied thereto by moving the transducer in a selected direction relative to the membrane and the compressed breast while sending ultrasound energy from the transducer into the breast and receiving ultrasound energy returned to the transducer from the breast; computer-processing the ultrasound energy received by the transducer from the breast to generate initial ultrasound breast images conforming to planes that are generally transverse to said chestward direction; further computer-processing said initial ultrasound breast images to generate further ultrasound images of the breast that conform to planes transverse to the planes of the initial ultrasound images; selectively displaying at least some of said initial and/or further ultrasound images of the patient's breast; and moving the scanning assembly out of contact with the patient's breast, to a non-scanning position and removing the membrane from the assembly. 